Incremento selettivo delle pseudomonadi fluorescenti indigene attraverso il trattamento chimico delle acque irrigue ricircolanti: un approccio integrato per il controllo delle fitopatie e la promozione della crescita delle piante nei sistemi fuori suolo
Author(s)
Pagliaccia, Deborah
Date Issued
October 8, 2008
Type
Doctoral Thesis
Abstract
Zoosporic root-infecting pathogens are the most destructive organisms in recirculating hydroponic systems. Strategies proposed for eliminating these pathogens from recycled nutrient solution include: filtration, sedimentation, chlorination, ozonation, heat, UV light, and the application of antimicrobial chemicals or biocontrol agents. The latter strategy has been investigated extensively but inconsistent performance in disease abatement following their employment has been a problem due to the inability of the biocontrol agent to maintain a critical threshold population necessary for sustained activity.
Amendment of the recycled nutrient solution with specific carbon substrates (i.e., synthetic and natural nitrification inhibitors) resulted in the selective enhancement of indigenous pseudomonad populations to the presumed threshold levels. We verified the ubiquity of that response in several hydroponic systems with different host plants and, most significantly, we document, for the first time, significant and sustained disease abatement. A combination of traditional (plate counting) and culture-independent methods (T-RFLP and BiologTM assay) suggested that nitrification inhibitors selectively increased P. putida and reduced bacterial diversity in the nutrient solution. The enhanced indigenous pseudomonad also colonized roots. An introduced biocontrol agent, P. fluorescens Pf5, showed no competitive advantage over the native pseudomonad. Additionally, we demonstrated that the active ingredient in the nitrification inhibitors exerted direct antifungal activity whereas inert ingredients had indirect role in disease suppression via the enhanced pseudomonad population. In general, amendment of the recycled nutrient solution with nitrification inhibitors had a stabilizing effect on pH and electrical conductivity and promising positive effects on plant growth and yield.
Cumulatively, our results support the hypothesis that it is possible to modify the environment to make it more conducive to the survival of indigenous bacteria. Many, if not most, habitats already contain prospective members who, if enhanced, could function as biocontrol agents.
Additional information
Dottorato di ricerca in Ortoflorofrutticoltura
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